Development and characterization of two novel 68 Ga-labelled neuropeptide Y short analogues with potential application in breast cancer imaging.

In vivo receptor targeting with radiolabelled peptide-based probes is an attractive approach for the development of novel radiotracers for molecular imaging. This work presents the development and characterization of two novel neuropeptide Y analogues labelled with a positron emitter 68 Ga, for potential use in breast cancer imaging. Both analogues share the same amino acid sequence and were derivatized with NOTA through either a lysine linker (L1) or an acetylated lysine (L2). In both cases, a single product with radiochemical purity higher than 95% was obtained. The two complexes were hydrophilic, showed remarkable in vitro stability, good cellular uptake, binding affinity in the nanomolar range and high cellular internalization rate. Biodistribution studies revealed low blood uptake and elimination through the urinary tract. The addition of an acetyl group in the spacer increased the lipophilicity of C2 and modified the reactivity of the ε-amino group of the lysine which resulted in lower protein binding and lower percentage of injected dose in bladder and urine. The tumour versus muscle ratio was (3.8 ± 0.4) for 68 Ga-L1 and (4.7 ± 0.4) for 68 Ga-L2. These results encourage performing further studies in order to complete the evaluation of both tracers as potential radiopharmaceutical for breast cancer imaging.

Development and characterization of a 99m Tc-labeled Neuropeptide Y short analog with potential application in breast cancer imaging.

The aim of this work was to develop and evaluate a 99m Tc-labeled neuropeptide Y derivative with affinity toward Y1-receptor. The selected amino acid sequence included nine amino acids derived from the C-terminal portion of the NPY complemented with the addition of one cysteine-mercaptoacetic acid moiety to bind the radiometal. Labeling was achieved through the preparation of a 3 + 1 nitrido complex. Physicochemical evaluation, cell uptake, internalization and externalization studies, and competitive assays were performed. Biodistribution experiments were carried out in normal and tumor-bearing mice. A single product with radiochemical purity >90% and high stability was obtained. In vitro analysis showed specific cellular uptake, IC50 of 73.2 nM, and a high internalization rate (80%). Biodistribution studies showed low blood and renal uptake and combined hepatobiliary and urinary elimination. Preliminary studies in mice bearing induced breast tumors rendered promising uptake values.